Like most progressives, Bill de Blasio is a champion of public financing for political campaigns. And with good reason.

For all his railing against the evil of big money in politics, he’s been quick to take advantage of big fat donations to fuel his agenda — provided they come in a way that doesn’t require him to leave his fingerprints on them.

Take the Campaign for One New York.

This is an organization that grew out of de Blasio’s campaign for mayor, is run by his former campaign associates and now lobbies only for his policies. Yet he insists it’s independent.

Recently, the organization disclosed that it has accepted donations from people or groups who do business with the city.

Donors include businessmen from real-estate developer Donald Capoccia to Google founder Eric Schmidt. But the really big bucks came from — you guessed it — public-sector unions. The largest came from the American Federation of Teachers, parent organization of the United Federation of Teachers. The $350,000 contribution came just before the city came to terms with the UFT on generous teachers contract.

The next largest came from 1199 SEIU, which donated $250,000 and also represents many government workers.

When asked if he is comfortable with this, Mayor Bill went straight to the legalities. His personal campaign and Campaign for One New York are, he said, “very different realities.” He also noted that while campaign-finance laws generally impose limits on contributions to the campaigns of individual candidates, “when you’re talking about an issue-oriented organization, it’s a different approach.”

He’s right about that. The Campaign for One New York is a 501(c)4, which is devoted to issues and not individuals.

In principle, we have no problem with these groups. But there sure seems to be a double standard. Back when the 501(c)4s in question were conservative, we had Democrats such as Sen. Chuck Schumer demanding investigations and the IRS targeting them for special treatment.

But when the leaders of public-sector unions have their parent organizations make six-figure deposits into a Democratic mayor’s pet lobbying group, even while they are negotiating with him over their own salaries and benefits, suddenly it’s no longer a problem.